If you’ve been using Firefox 3, you may have noticed one glaring hole: instead of letting you view PDFs directly in the browser, it forces you to download them when you click on a PDF link. To get around this behaviour, check out the free, new firefox-mac-pdf plug-in, which works on both PowerPC and Intel Macs. (It requires Mac OS X 10.4 or later.)
Click on the site’s Install PDF Plugin link and then select the Allow button that pops up at the top of your browser window. (Firefox blocks installation until you give it permission.) Restart Firefox, and you’ll now be able to view PDFs directly in the browser. (Oddly, the plug-in is called Quartz PDF Plugin in the Firefox Extensions screen.)
While perusing a PDF within Firefox, you can right-click on it to access a contextual menu with a number
of viewing options, including controls for zooming and toggling between single pages and spreads. You can also employ Firefox’s built-in zoom features (via the View menu or using keyboard shortcuts), and navigate up and down with the use of the arrow keys.